Source: BBC calculations on data from UK Kennel Club and US Veterinary Medical Database

The calculator uses these multipliers for the first two years of a dog's life:

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Meg, my West Highland Terrier died a couple of months ago. She'd reached the grand old age of 19 years and four months.

A few days later, I was reminded of the oft-quoted statistic that every human year equates to seven dog years. But if that stat were really true then Meg would have been 135 years old when she died, which seems very unlikely.

The calculator does not work for cross breeds, sadly, but on average these live 1.22 years longer than pure breeds, according to Dan O'Neill (from Petts Wood in London...) who is researching the subject for a PhD at the Royal Veterinary College.

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Nor does the calculator work for cats. What we can say is that the average life expectancy of a cat is 12.1 years, which equates to 64 human years.

Guidelines issued by the American Association of Feline Practitioners say that cats reach 10 human years in their first six months and are approximately 24 at the age of two years. After this their age increases by four "cat years" every year.